Download Chronic Lymphocytic Leukemia

Chronic Lymphocytic Leukemia
Kristi S. Lively, DVM, DABVP
BASIC INFORMATION
Description
Chronic lymphocytic leukemia (CLL) is a cancer of lymphocytes,
a type of white blood cell (WBC). Lymphocytes are formed in the
bone marrow and other lymphoid organs. When malignant proliferation occurs, these cells are released into the bloodstream.
With CLL, so many cancerous lymphocytes are released into
the blood that the WBC count becomes very elevated (leukocytosis). Leukocytosis can occur in response to infection, stress, or
inflammation but with these conditions the WBCs appear normal. Leukemia differs from other forms of leukocytosis in that the
WBCs being produced are abnormal and represent a malignancy.
Lymphocytic leukemia may be acute (sudden in onset) or
chronic (developing slowly), depending on the stage of the lymphocyte precursor involved. Acute leukemia forms when immature blast cells proliferate, whereas chronic leukemia involves
more developed lymphocytes. In general, acute leukemia is more
aggressive than CLL. CLL is a slowly progressive disease, often
of older dogs and cats.
Causes
The cause of CLL has not been identified in either dogs or cats.
CLL in dogs tends to involve a particular type of lymphocyte,
called the T cell. CLL is rare in cats.
Clinical Signs
About 50% of patients with CLL have no clinical signs, and the
disease is discovered when a blood count is done for another
reason. Lethargy is the most common sign. Other signs include
weight loss, loss of appetite, and enlargement of the spleen, liver,
or lymph nodes (glands). Vomiting or diarrhea may be present if
the gastrointestinal tract is affected.
A condition called hyperviscosity syndrome is a potential complication of CLL and arises when the lymphocytes produce a protein that builds up in the blood. The malignant lymphocytes all tend
to form the same type of protein, which is a monoclonal antibody.
Excessive levels of these proteins cause the blood to thicken and may
cause small blood vessels to bleed. Signs of hyperviscosity syndrome
may include nose bleeds, seizures, blurred vision, or blindness.
Diagnostic Tests
The complete blood count (CBC) reveals a persistent, unexplained,
elevated lymphocyte count. Sometimes the count is so elevated the
diagnosis of leukemia is obvious. However, CLL can be confused
with leukocytosis from other causes if the lymphocyte count is
only moderately elevated. Low blood counts of red blood cells
(anemia) and neutrophils (another type of WBC) may also occur.
It may be necessary to submit a blood sample for further analysis
if the diagnosis of leukemia is not definite. Special stains and tests
may be performed to identify the cancer cells and their stage of
development.
A protein electrophoresis test may be done to confirm that
blood protein is elevated and to determine whether the protein is
a monoclonal antibody. A bone marrow aspiration may be recommended to evaluate the various cells present in the marrow and to
confirm the identity of the cancerous cells. A fine-needle aspiration or biopsy of enlarged lymph nodes may be needed to differentiate leukemia from lymphoma, another cancer of lymphocytes.
Other laboratory tests, x-rays, and possibly an ultrasound may
be recommended to assess involvement of other organs, to rule out
other causes of leukocytosis, and to differentiate CLL from acute
lymphocytic leukemia, other forms of lymphoma, and other types
of leukemia.
TREATMENT AND FOLLOW-UP
Treatment Options
Since the course of this disease is very slowly progressive, treatment may not be indicated at the time of diagnosis. If the lymphocyte count is less than 60,000-75,000 cells per microliter (µL)
and the patient has no abnormalities in other blood cells, treatment
may be delayed. Treatment is usually started right away if clinical
signs develop, if hyperviscosity syndrome is detected, if the lymphocyte count rises above 75,000/µL, or if anemia, low platelet
counts, or low neutrophil counts occur.
Chemotherapy is the treatment of choice, and protocols may
include drugs such as chlorambucil, prednisone, and vincristine.
Occasionally other supportive treatments are needed, depending
on the animal’s clinical signs and the presence of other abnormal
laboratory results.
Follow-up Care
If no treatment is started, the CBC is repeated periodically to monitor the lymphocyte count. During chemotherapy, CBCs are also
rechecked to assess response to treatment and to monitor for side
effects from the chemotherapeutic medications.
Prognosis
Prognosis for remission is good, with survival times of 2-3 years
being common. Even without chemotherapy, patients may live 1-2
years beyond diagnosis. In some animals, chemotherapy may be
stopped if remission lasts for longer than 1 year.
If you have other questions or concerns about this, or other health topics, please call
McFarland Animal Hospital
608-838-3400
Copyright © 2011 by Saunders, an imprint of Elsevier Inc. All rights reserved.